Heat exchanger

ABSTRACT

A plurality of heat-exchange tubes  30  each including a flat pipe including a groove  36  and wavelike depression-and-projection portions  33, 34  are arranged in parallel in such a manner that each of respective longitudinal directions thereof is a vertical direction, and a heat exchange medium is made to flow from an inlet  31  at each lower portion to an outlet  32  at each upper portion. Guide walls  43, 44  are provided in a shell  40 , and exhaust gas is made to flow an inlet  41  at an upper portion to an outlet  42  at a lower portion, thereby making the exhaust gas meander in flow paths  46   a  to  46   d  and a space between the plurality of heat-exchange tubes  30 . The exhaust gas and the heat exchange medium have flows opposed to each other as a whole, and a secondary flow of the exhaust gas is made to occur by the wavelike depression-and-projection portions  33, 34 , thereby enhancing the heat exchange efficiency, and the arrangement in such a manner that each of the longitudinal directions is the vertical direction and the formation of a groove  36  and the wavelike depression-and-projection portions  33, 34  enable acceleration of downward discharge of condensed water.

TECHNICAL FIELD

The present invention relates to a heat exchanger and specifically relates to a finless heat exchanger that recovers heat of exhaust gas, which results from combustion, via heat exchange with a heat exchange medium.

BACKGROUND ART

Conventionally, for this type of heat exchanger, one in which cooling water is made to flow in a plurality of tubes each formed into a U-shape and exhaust gas is made to flow substantially perpendicular to the cooling water in the plurality of tubes from the side of the plurality of tubes close to outlets for the cooling water, thereby recovering heat of the exhaust gas (see, for example, non-patent literature 1). In this heat exchanger, i.e., the plurality of tubes are formed using stainless steel to prevent corrosion caused by exhaust gas, and corrugated fins are inserted between the plurality of tubes to enhance the heat exchange efficiency.

CITATION LIST Non Patent Literature

-   Non Patent Literature 1: Transactions of the Japan Society of     Mechanical Engineers, Series B, Vol. 72, No 713, pp. 96-103, 2006

DISCLOSURE OF THE INVENTION

Where a heat exchanger for latent heat recovery, which recovers heat of exhaust gas, is downsized, the heat exchange efficiency may be lowered by condensed water resulting from heat exchange with the exhaust gas.

Although a heat exchanger is downsized by flattening the tubes and reducing the spaces between the tubes to enhance the efficiency of heat exchange with exhaust gas, if the spaces between the tubes are reduced, the condensed water remains between the tubes, hindering the flow of the exhaust gas, which results in a decrease in heat exchange efficiency. In particular, in a heat exchanger with fins attached between the tubes, the fins hinder discharge of condensed water, resulting in a significant decrease in heat exchange efficiency in addition to a decrease in fin efficiency.

A main object of a heat exchanger according to the present invention is to achieve downsizing and enhancement of heat exchange efficiency of a heat exchanger for a heat exchanger for latent heat recovery, which recovers heat of exhaust gas.

The present invention accomplishes at least part of the demands mentioned above and the other relevant demands by the following configurations applied to the heat exchanger.

The present invention is directed to a finless heat exchanger for recovering heat of exhaust gas resulting from combustion via heat exchange between the exhaust gas and a heat exchange medium. The heat exchanger includes a plurality of heat-exchange tubes each formed as a flat pipe using a metal plate material having an excellent acid corrosion resistance. The plurality of heat-exchange tubes is arranged in parallel in such a manner that each of respective longitudinal directions thereof is mainly a vertical direction. The finless heat exchanger further includes a shell that houses the plurality of heat-exchange tubes and forms a flow path for the exhaust gas to pass therethrough between the plurality of heat-exchange tubes and the shell. The plurality of heat-exchange tubes each include an inlet for the heat exchange medium at a vertically lower portion thereof and an outlet for the heat exchange medium at a vertically upper portion thereof. The shell includes an inlet for the exhaust gas at a vertically upper portion thereof and an outlet for the exhaust gas at a vertically lower portion thereof. The plurality of heat-exchange tubes and/or the shell include a meandering guiding section formed so that the exhaust gas flows in a space between the plurality of heat-exchange tubes while meandering downward from the vertically upper portion.

In the heat exchanger according to the present invention, a plurality of heat-exchange tubes each formed as a flat pipe using a metal plate material having an excellent acid corrosion resistance are arranged in parallel in such a manner that each of respective longitudinal directions thereof is mainly a vertical direction, and the plurality of heat-exchange tubes arranged are housed in a shell. Consequently, a flow path for exhaust gas to pass through is formed between the shell and the plurality of heat-exchange tubes. The plurality of heat-exchange tubes each include an inlet for a heat exchange medium at a vertically lower portion thereof and an outlet for the heat exchange medium at a vertically upper portion thereof, and the shell includes an inlet for the exhaust gas at a vertically upper portion thereof and an outlet for the exhaust gas in a vertically lower portion thereof. Then, a meandering guiding section is formed in either or both of the plurality of heat-exchange tubes and the shell so that the exhaust gas flows in spaces between the plurality of heat-exchange tubes while meandering downward from the vertically upper portion. As described above, a plurality of heat-exchange tubes formed as flat pipes are arranged in parallel and housed in a shell, enabling provision of a small-size heat exchanger.

In the heat exchanger according to the present invention configured as described above, a heat exchange medium flows in from the inlets formed at the vertically lower portions of the plurality of heat-exchange tubes and flow in the plurality of heat-exchange tubes arranged in parallel from the vertically lower portions to the vertically upper portions, and flows out from the outlets formed at the vertically upper portions of the plurality of heat-exchange tubes. Meanwhile, exhaust gas flows in from the inlet formed at the vertically upper portion of the shell, flows in the flow path formed between the shell and the plurality of heat-exchange tubes, and flows out from the outlet formed at the vertically lower portion of the shell. In the flow path formed between the shell and the plurality of heat-exchange tubes, the exhaust gas flows in the spaces between the plurality of heat-exchange tubes while meandering downward from the vertically upper portion via the meandering guiding section formed in either or both of the plurality of heat-exchange tubes and the shell. Accordingly, the heat exchange medium flows from the vertically lower portions to the vertically upper portions, while the exhaust gas flows from the vertically upper portion to the vertically lower portion as a whole although the exhaust gas is made to meander by the meandering guiding section, and thus, the heat exchange medium and the exhaust gas have flows opposed to each other, enhancing the heat exchange efficiency. As a result of heat exchange with the exhaust gas, condensed water is generated on flat surfaces of the plurality of heat-exchange tubes, however, the plurality of heat-exchange tubes are arranged in parallel in such a manner that each of the respective longitudinal directions thereof is mainly the vertical direction, and thus, the condensed water is collected toward the vertically lower portions and discharged. Consequently, the generated condensed water can be prevented from remaining and hindering the flow of the exhaust gas, and thus, the pressure loss of the exhaust gas can be reduced. Furthermore, since the heat exchanger according to the present invention is configured as a finless heat exchanger, the discharge of condensed water can be accelerated compared to those with fins attached between the plurality of heat-exchange tubes. Consequently, a heat exchanger having a small size and good heat exchange efficiency can be provided.

In the heat exchanger according to the present invention, the plurality of heat-exchange tubes can each include a vertical groove at a substantial center of a flat surface thereof. Consequently, condensed water generated on the flat surfaces of the plurality of heat-exchange tubes flows along the grooves to the vertically lower portions, enabling enhancement of the condensed water discharge performance, and thus, a heat exchanger having a small size and good heat exchange efficiency can be provided. Furthermore, as a result of formation of the grooves, the strength of the plurality of heat-exchanges can be enhanced. Consequently, the plurality of heat-exchange tubes can be formed using a thinner metal plate material. In such case, the groove in each of the plurality of heat-exchange tubes can be fixed by bonding inside the heat-exchange tube. Consequently, the strength of the plurality of heat-exchange tubes can further be enhanced.

In the heat exchanger according to the present invention, the meandering guiding section can include a guide wall formed inside the shell so that the exhaust gas flows in a substantially horizontal direction orthogonal to the plurality of heat-exchange tubes. In this case, the meandering guiding section can further include a rib formed toward the guide wall at a flat surface of each of the plurality of heat-exchange tubes at a position aligned with the guide wall of the shell, in addition to the guide wall. Consequently, the exhaust gas can be made to more reliably flow in the spaces between the plurality of heat-exchange tubes while meandering, enabling enhancement in heat exchange efficiency.

Further, in the heat exchanger according to the present invention, the meandering guiding section can include a plurality of ribs formed at a plurality of positions in a substantially horizontal direction on a flat surface of each of the plurality of heat-exchange tubes, and an inner side of an outer wall of the shell can be in contact with one side surface and another side surface alternately from an uppermost position to a lower position from among opposite side surfaces of the plurality of heat-exchange tubes at positions where the plurality of ribs are formed and is not in contact with a side surface opposite to the side surface that is in contact with the inner side from among opposite side surfaces at a same position. Consequently, the plurality of ribs formed on the flat surfaces of the heat-exchange tubes and the shell can make the exhaust gas flow in the spaces between the plurality of heat-exchange tubes while meandering without forming guide walls inside the shell, enabling enhancement of the heat exchange efficiency.

Alternatively, in the heat exchanger according to the present invention, the plurality of heat-exchange tubes can each include a plurality of wavelike depression-and-projection portions formed over a substantial entirety of a flat surface thereof, each of the plurality of wavelike depression-and-projection portions including a depression portion and a projection portion flexed at an angle ranging from 10 to 80 degrees relative to a main flow direction of the exhaust gas to be continuous with each other. When the exhaust gas flows in the spaces between the plurality of heat-exchange tubes, the exhaust gas flows accompanied by a secondary flow caused by the plurality of wavelike depression-and-projection portions formed on the flat surfaces of the plurality of heat-exchange tubes. Consequently, the heat exchange efficiency is enhanced. Furthermore, the condensed water is guided to the depression portions of the wavelike depression-and-projection portions by means of the flow of the exhaust gas and the effect of the surface tension, and thus, the depression portions of the wavelike depression-and-projection portions have the role of a discharge flow path for the condensed water. In other words, formation of the wavelike depression-and-projection portions at the flat surfaces of the plurality of heat-exchange tubes enables enhancement of the condensed water discharge performance.

In the heat exchanger that includes a plurality of wavelike depression-and-projection portions formed over a flat surface of plurality of heat-exchange tubes according to the present invention, the plurality of heat-exchange tubes can be each formed so that an angle of the wavelike depression-and-projection portions in a region positioned in a vertically upper portion of the flat surface relative to the main flow direction of the exhaust gas is smaller than an angle of the wavelike depression-and-projection portions in a region positioned in a vertically lower portion of the flat surface relative to the main flow direction of the exhaust gas. As a result of making the angle of the wavelike depression-and-projection portion in the region positioned in each of the vertically upper portions of the flat surfaces of the plurality of heat-exchange tubes relative to the direction of the main flow of the exhaust gas be small, the secondary flow of the exhaust gas can be accelerated, enabling enhancement of the efficiency of heat exchange between the exhaust gas and the heat exchange medium, and as a result of making the angle of the wavelike depression-and-projection portion in the region positioned in each of the vertically lower portions of the flat surfaces of the plurality of heat-exchange tubes relative to the direction of the main flow of the exhaust gas be large, an angle of the depression portions of the wavelike depression-and-projection portions relative to the vertical direction can be made to be small, enabling condensed water to easily flow to the vertically lower portions. In this case, the plurality of heat-exchange tubes can be each formed so that the angle of the wavelike depression-and-projection portions in the region positioned in the vertically upper portion of the flat surface relative to the main flow direction of the exhaust gas falls within a range of 10 to 45 degrees and the angle of the wavelike depression-and-projection portions in the region positioned in the vertically lower portion of the flat surface relative to the main flow direction of the exhaust gas falls within a range of 45 to 80 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating a schematic configuration of a heat exchanger 20 in one embodiment of the invention;

FIG. 2 is a side view of an outer appearance of a plurality of heat-exchange tubes 30 used in the heat exchanger 20;

FIG. 3 is an enlarged diagram illustrating a heat-exchange tube 30 with a part thereof enlarged;

FIG. 4 is a pattern diagram illustrating a flow of an exhaust gas in the heat exchanger 20 of the invention;

FIG. 5 schematically illustrates the configuration of another heat exchanger 20B in one modified example;

FIG. 6 schematically illustrates the configuration of another heat exchanger 20C in another modified example;

FIG. 7 schematically illustrates the configuration of another heat exchanger 20D in another modified example;

FIG. 8 schematically illustrates the configuration of another heat exchanger 20E in another modified example;

FIG. 9 schematically illustrates the configuration of another heat-exchange tube 30F in one modified example;

FIG. 10 schematically illustrates the configuration of another heat exchanger 20G in one modified example.

BEST MODES OF CARRYING OUT THE INVENTION

One mode of carrying out the invention is discussed below as a preferred embodiment.

FIG. 1 is a configuration diagram illustrating a schematic configuration of a heat exchanger 20, which is an embodiment of the present invention; FIG. 2 is a side view of an outer appearance of a plurality of heat-exchange tubes 30 used in the heat exchanger 20 according to the embodiment; FIG. 3 is an enlarged diagram illustrating a heat-exchange tube 30 with a part thereof enlarged. The heat exchanger 20 according to the embodiment is configured as a finless heat exchanger that recovers heat of exhaust gas resulting from combustion via heat exchange between the exhaust gas and a heat exchange medium such as cooling water, and as illustrated, includes a plurality of (for example, 22) heat-exchange tubes 30 arranged in parallel in such a manner that each of respective longitudinal directions thereof is a vertical direction, and a shell 40 that houses the plurality of heat-exchange tubes 30.

Each heat-exchange tube 30 is formed as a flat pipe using a plate material having a thickness of 0.3 mm and including a metal material having an excellent acid corrosion resistance (for example, stainless steel), the flat pipe having a substantially rectangular shape in its entirety, which has a height (length) of 150 mm, a width of 30 mm and an inner heat exchange medium flow path thickness of 2.4 mm (an entire thickness of 3.0 mm including the thickness of the plate), and is arranged in parallel with an adjacent heat-exchange tube 30 so as to provide a space of 1.6 mm therebetween in such a manner that the longitudinal direction thereof is the vertical direction. An inlet 31 for a heat exchange medium is formed in the vicinity of a lower end of a vertically lower portion of each heat-exchange tube 30, and the respective inlets 31 of the respective heat-exchange tubes 30 communicate with one another via a connecting pipe 31 a. Also, an outlet 32 for the heat exchange medium is formed in the vicinity of an upper end of a vertically upper portion of each heat-exchange tube 30, and the respective outlets 32 of the respective heat-exchange tubes 30 via a connecting pipe 32 a. Accordingly, a heat exchange medium flows in from the respective inlets 31 positioned in the vertically lower portions of the respective heat-exchange tubes 30, flows in the respective heat-exchange tubes 30 toward the vertically upper portions, and flows out from the respective outlets 32 positioned in the vertically upper portions of the respective heat-exchange tubes 30.

At a center of each flat surface of each heat-exchange tube 30, as illustrated in FIGS. 1 and 3, a vertical groove 36 projecting inward, the groove 36 having a depth of 1.2 mm and a width of 1.6 mm is formed. Since the groove 36 is formed in each of the opposite flat surfaces of the heat-exchange tube 30, the grooves 36 at the opposite flat surfaces are in contact with each other. In the embodiment, the grooves 36 at the opposite flat surfaces, the grooves 36 being in contact with each other inside the tube, are fixed by bonding using, e.g., brazing. Consequently, the strength of the heat-exchange tubes 30 can be enhanced. Furthermore, the grooves 36 each collect condensed water generated on the surfaces of the respective heat-exchange tube 30 as a result of heat exchange with exhaust gas and guide the condensed water to the respective vertically lower portion, enabling enhancement of the condensed water discharge performance.

Furthermore, wavelike depression-and-projection portions 33, 34 each including depression portions 33 and projection portions 34 having a shape formed by making “V” or “W”-shapes be continuous with one another by rotating the “V” or “W”-shapes by 90 degrees, the “V” or “W”-shapes being flexed at a predetermined angle α relative to a horizontal direction are formed over an entirety of each flat surface of each heat-exchange tube 30. The angle α of the wavelike depression-and-projection portions 33, 34 relative to the horizontal direction falls within a range of 10 to 80 degrees, preferably a range of 30 to 60 degrees, more preferably a range of 30 to 45 degrees, and is 30 degrees in the embodiment. The wavelike depression-and-projection portions 33, 34 formed at each flat surface of each heat-exchange tube 30, upon exhaust gas flowing substantially horizontally, makes a secondary flow of the exhaust gas occur in addition to a main flow of the exhaust gas. Thus, the efficiency of heat exchange between the exhaust gas and the heat exchange medium can be enhanced. Furthermore, the wavelike depression-and-projection portions 33, 34 make the condensed water adhered thereto by the flow of the exhaust gas and the effect of the surface tension be collected in the depression portions 33, and further guided to the respective vertically lower portions, enabling the condensed water discharge performance.

The shell 40 is formed as a case having a substantial rectangular parallelepiped shape that houses the plurality of heat-exchange tubes 30 connected via the connecting pipes 31 a, 32 a, using a plate material having a thickness of 0.3 mm and including a metal material having an excellent acid corrosion resistance (for example, stainless steel) as with the respective heat-exchange tubes 30, and forms flow paths 46 a, 46 b, 46 c, 46 d for exhaust gas jointly with the plurality of heat-exchange tubes 30. On the left side in FIG. 1 of a vertically upper portion of the shell 40, an inlet 41 for exhaust gas is formed, and on the right side in FIG. 1 of a vertically lower portion of the shell 40, an outlet for the exhaust gas is formed. Furthermore, inside the shell 40, guide walls 43, 44 that separate the flow paths 46 a, 46 b, 46 c, 46 d for exhaust gas, which are formed jointly with the plurality of heat-exchange tubes and guide the flow of exhaust gas are attached. Accordingly, as indicated by the white arrows in FIG. 4, exhaust gas flows in from the inlet 41 formed at the vertically upper portion of the shell 40, passes through the spaces between the plurality of heat-exchange tubes 30 and the flow paths 46 a, 46 b, 46 c, 46 d while meandering, and flows out from the outlet 42 formed at the vertically lower portion of the shell 40. Accordingly, the exhaust gas and the heat exchange medium flowing in the plurality of heat-exchange tubes 30 have flows opposed to each other as a whole, enabling enhancement of the heat exchange efficiency.

In the heat exchanger 20 according to the above-described embodiment, a plurality of heat-exchange tubes 30, each having a substantially rectangular shape and formed as a flat pipe, are arranged in parallel at an interval of 1.6 mm in such a manner that each of the respective longitudinal directions thereof is a vertical direction, the heat exchange medium is made to flow in from the respective inlets 31 positioned at the vertically lower portions, flow in the respective heat-exchange tubes 30 toward the vertically upper portions, and flow out from the respective outlets 32 positioned at the vertically upper portions of the respective heat-exchange tubes 30. Meanwhile, the exhaust gas is made to flow in from the inlet 41 formed at the vertically upper portion of the shell 40, flow in the flow paths 46 a, 46 b, 46 c, 46 d formed by the shell 40, the plurality of heat-exchange tubes 30 and the guide walls 43, 44 and the spaces between the plurality of heat-exchange tubes 30 while meandering, and flow out from the outlet 42 formed at the vertically lower portion of the shell 40, whereby the exhaust gas and the heat-exchange medium flowing in the plurality of heat-exchange tubes 30 have flows opposed to each other as a whole, enabling enhancement of the heat exchange efficiency. As a result of arranging the plurality of heat-exchange tubes 30 in parallel in such a manner that each of the longitudinal directions thereof is the vertical direction, condensed water generated on the flat surfaces of the plurality of heat-exchange tubes 30 as a result of heat exchange with the exhaust gas is collected toward the vertically lower portions and discharged. Consequently, the generated condensed water can be prevented from remaining and hindering the flow of the exhaust gas, enabling reduction of the pressure loss of the exhaust gas. In addition, since the heat exchanger 20 according to embodiment is configured as a finless heat exchanger, discharge of condensed water can be accelerated compared to those with fins attached between a plurality of heat-exchange tubes 30. Consequently, a heat exchanger having a small size and good heat exchange efficiency can be provided.

Furthermore, in the heat exchanger 20 according to the embodiment, as a result of forming the vertical groove 36 at a center of each of the flat surfaces of the heat-exchange tubes 30, condensed water generated on the flat surfaces of the heat-exchange tubes 30 as a result of heat exchange with the exhaust gas can be collected and guided to the vertically lower portions, enabling enhancement of the condensed water discharge performance, and the strength of the plurality of heat-exchange tubes 30 can be enhanced, and the plurality of heat-exchange tubes 30 can be formed using a metal material having a small thickness, whereby a heat exchanger having a smaller size can be provided. In addition, the grooves are fixed by bonding inside the respective tubes, enabling enhancement of the strength of the heat-exchange tubes 30.

Furthermore, in the heat exchanger 20 according to the embodiment, as a result of forming the wavelike depression-and-projection portions 33, 34 over an entirety of each of the flat surfaces of the plurality of heat-exchange tubes 30, the wavelike depression-and-projection portions 33, 34 including the depression portions 33 and the projection portions 34 flexed at the predetermined angle α relative to a horizontal direction in which the exhaust gas mainly flow to be continuous with one another, a secondary flow of the exhaust gas can be made to occur in addition to the main flow thereof, and consequently, the efficiency of heat exchange between the exhaust gas and the heat exchange medium can be enhanced. Furthermore, the wavelike depression-and-projection portions 33, 34 collect condensed water adhered thereto by the flow of the exhaust gas into the depression portions 33 and guide the condensed water to the vertically lower portions, enabling further enhancement of the condensed water discharge performance.

Although the heat exchanger 20 according to the embodiment includes the groove 36 formed at the center of each of the flat surfaces of the plurality of heat-exchange tubes 30 and the wavelike depression-and-projection portions 33, 34 formed over the substantial entirety of the flat surface, as in a heat exchanger 20B according to an alteration in FIG. 5, it is possible that a groove 36 is formed at a center of each of flat surfaces of a plurality of heat-exchange tubes 30B but no wavelike depression-and-projection portions 33, 34 are formed at the flat surface, and conversely, as in a heat exchanger 20C according to an alteration in FIG. 6, it is possible that no groove 36 is formed at a center of each of flat surfaces of heat-exchange tubes 30C but wavelike depression-and-projection portions 33C, 34C are formed at the flat surface. In this case, the wavelike depression-and-projection portions 33C, 34C may be formed also at the center of each of the flat surfaces of the plurality of heat-exchange tubes 30C. Alternatively, it is possible that neither groove 36 nor wavelike depression-and-projection portions 33, 34 are formed at each of the flat surfaces of the plurality of heat-exchange tubes.

Although the heat exchanger 20 according to the embodiment includes the groove 36 formed at the center of each of the flat surfaces of the plurality of heat-exchange tubes 30 and the wavelike depression-and-projection portions 33, 34 formed over the substantial entirety of the flat surface, as in a heat exchanger 20D according to an alteration in FIG. 7, ribs 37 a to 37 d, which project outward, may be formed at positions in each of flat surfaces of a plurality of heat-exchange tubes 30D, the positions being aligned with guide walls 43, 44. Consequently, meandering of exhaust gas can be guided more reliably. In this case, the adjacent ribs 37 a and rib 37 b, and the adjacent ribs 37 c and rib 37 d are preferably separated, respectively, by a groove 36. Thus, where ribs are formed at positions at the flat surface of the plurality of heat-exchange tubes 30D, the positions being aligned with the guide walls 43, 44, as in a heat exchanger 20E according to an alteration in FIG. 8, only ribs 37 a, 37 d extending from respective parts of each of the flat surfaces of the plurality of heat-exchange tubes 30E, the parts being adjacent to the guide walls 43, 44, to the groove 36 may be formed.

Although in the plurality of heat-exchange tubes 30 in the heat exchanger 20 according to the embodiment, the angle α of the wavelike depression-and-projection portions 33, 34 formed at the flat surfaces relative to the horizontal direction is 30 degrees, the angle α only needs to fall within a range of 10 to 80 degrees, preferably a range of 30 to 60 degrees. Also, as in a heat-exchange tube 30F according to an alteration in FIG. 9, it is possible that an angle α of wavelike depression-and-projection portions 33Fa, 34Fa positioned on the exhaust gas inflow side relative to the horizontal direction is small, and an angle β of wavelike depression-and-projection portions 33Fb, 34Fb positioned in the exhaust gas outflow side relative to the horizontal direction is larger than the angle α. For example, the angle α is preferably 10 to 45 degrees and the angle β is preferably 45 to 80 degrees. The heat-exchange tube 30F according to the alteration, an angle of 30 degrees is employed for the angle α and an angle of 60 degrees is employed for the angle β. This is based on setting of the angle α so as to accelerate a secondary flow of exhaust gas to enhance the heat exchange efficiency for the wavelike depression-and-projection portions 33Fa, 34Fa positioned on the exhaust gas inflow side and setting of the angle β so as to accelerate downward discharge of condensed water for the wavelike depression-and-projection portions 33Fb, 34Fb positioned on the exhaust gas outflow side. Accordingly, wavelike depression-and-projection portions 33, 34 may be formed in such a manner that the angles of the wavelike depression-and-projection portions 33, 34 relative to the horizontal direction are larger from the exhaust gas inflow side toward the exhaust gas outflow side successively or stepwise.

While in the heat exchanger 20 according to the embodiment, the plurality of heat-exchange tubes 30 are formed so as to be a flat pipe, using a plate material having a thickness of 0.3 mm and including stainless steel, the flat pipe having a substantially rectangular shape in its entirety, which has a height (length) of 150 mm, a width of 30 mm and an inner heat exchange medium flow path thickness of 2.4 mm (an entire thickness of 3.0 mm including the thickness of the plate), and are arranged in parallel so as to provide a space of 1.6 mm between respective adjacent heat-exchange tubes 30 in such a manner that each of the longitudinal directions thereof is the vertical direction, any plate material may be employed as long as such plate material is one including a metal material having an excellent acid corrosion resistance other than stainless steel, and the thickness of the plate material may be smaller or larger than 0.3 mm if the strength can be maintained. Also, the height, the width and the inner heat exchange medium flow path thickness are not limited to 150 mm, 30 mm and 2.4 mm, respectively, and any height, any width and any inner heat exchange medium flow path thickness may be employed as long as the inner heat exchange medium flow path thickness is no more than 3 mm. Furthermore, it is not essential that each of the plurality of heat-exchange tubes 30 have a shape of a substantially-rectangular flat hollow pipe, and the shape may be, for example, an oval flat hollow pipe. In addition, the interval of adjacent heat-exchange tubes 30 is not limited to 1.6 mm, and an interval with any size may be employed as long as such interval is no more than 3 mm. Furthermore, it is not essential that the plurality of heat-exchange tubes 30 be arranged in parallel in such a manner that each of the respective longitudinal directions thereof is exactly the vertical direction, and the plurality of heat-exchange tubes 30 may be arranged in parallel in such a manner that each of the respective longitudinal directions thereof is the vertical direction when a certain degree is added thereto.

Although in the heat exchanger 20 according to the embodiment, the shell 40 is formed as a case having a substantially-rectangular parallelepiped shape that houses the plurality of heat-exchange tubes 30 using a plate material having a thickness of 0.3 mm and including stainless steel, any plate material having an excellent acid corrosion resistance other than stainless steel may be employed, and the thickness of the plate material may be smaller or larger than 0.3 mm if the strength can be maintained.

Although in the heat exchanger 20 according to the embodiment, the shell 40 is formed as a case having a substantially-rectangular parallelepiped shape that houses the plurality of heat-exchange tubes 30, and the guide walls 43, 44 are provided inside the shell 40 so that exhaust gas flows in the spaces between the plurality of heat-exchange tubes 30 and the flow paths 46 a, 46 b, 46 c, 46 d while meandering, as in a heat exchanger 20G according to an alteration in FIG. 10, using a plurality of heat-exchange tubes 30D each including ribs 37 a to 37 d formed thereon, it is possible that the inner side of an outer wall of a shell 40G is in contact with side surfaces of the plurality of heat-exchange tubes 30D where the respective ribs 37 a are formed and side surface of the plurality of heat-exchange tubes 30D where the respective ribs 37 d are formed, that is, the inner side of the outer wall is in contact with one side surface (side surface at a position where the rib 37 a is formed) and another side surface (side surface at a position where the rib 37 d is formed) alternately from an uppermost position to lower positions from among opposite side surfaces of the plurality of heat-exchange tubes 30D at positions where the plurality of rib 37 a to 37 d are formed and is not in contact with side surfaces (side surface at positions where the ribs 37 b, 37 c are formed) opposite to the side surfaces that are in contact with the inner side of the outer wall (side surfaces at the positions where the ribs 37 a, 37 d are formed) from among the opposite side surfaces at same positions. Consequently, the plurality of ribs 37 a to 37 d formed on the flat surfaces of the plurality of heat-exchange tubes 30D and the shell 40G can make exhaust gas flow in spaces between the plurality of heat-exchange tubes 30D while meandering without forming guide walls inside the shell 40G, enabling enhancement of the heat exchange efficiency.

The embodiment and its applications discussed above are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is preferably applied to the manufacturing industries of heat exchangers. 

1. A finless heat exchanger for recovering heat of exhaust gas resulting from combustion via heat exchange between said exhaust gas and a heat exchange medium, the heat exchanger comprising: a plurality of heat-exchange tubes each formed as a flat pipe using a metal plate material having an excellent acid corrosion resistance, said plurality of heat-exchange tubes being arranged in parallel in such a manner that each of respective longitudinal directions thereof is mainly a vertical direction; and a shell that houses said plurality of heat-exchange tubes and forms a flow path for said exhaust gas to pass therethrough between said plurality of heat-exchange tubes and said shell, wherein said plurality of heat-exchange tubes each include an inlet for said heat exchange medium at a vertically lower portion thereof and an outlet for said heat exchange medium at a vertically upper portion thereof; wherein said shell includes an inlet for said exhaust gas at a vertically upper portion thereof and an outlet for said exhaust gas at a vertically lower portion thereof, and wherein said plurality of heat-exchange tubes and/or said shell include a meandering guiding section formed so that said exhaust gas flows in a space between the plurality of heat-exchange tubes while meandering downward from the vertically upper portion.
 2. A heat exchanger according to claim 1, wherein said plurality of heat-exchange tubes each include a vertical groove at a substantial center of a flat surface thereof.
 3. A heat exchanger according to claim 2, wherein said groove in each of said plurality of heat-exchange tubes is fixed by bonding inside the heat-exchange tube.
 4. A heat exchanger according to claim 1, wherein said meandering guiding section includes a guide wall formed inside said shell so that said exhaust gas flows in a substantially horizontal direction orthogonal to said plurality of heat-exchange tubes.
 5. A heat exchanger according to claim 4, wherein said meandering guiding section includes a rib formed toward said guide wall at a flat surface of each of said plurality of heat-exchange tubes at a position aligned with said guide wall of said shell, in addition to said guide wall.
 6. A heat exchanger according to claim 1, wherein said meandering guiding section includes a plurality of ribs formed at a plurality of positions in a substantially horizontal direction on a flat surface of each of said plurality of heat-exchange tubes; and wherein an inner side of an outer wall of said shell is in contact with one side surface and another side surface alternately from an uppermost position to a lower position from among opposite side surfaces of said plurality of heat-exchange tubes at positions where said plurality of ribs are formed and is not in contact with a side surface opposite to said side surface that is in contact with the inner side from among opposite side surfaces at a same position.
 7. A heat exchanger according to claim 1, wherein said plurality of heat-exchange tubes each include a plurality of wavelike depression-and-projection portions formed over a substantial entirety of a flat surface thereof, each of said plurality of wavelike depression-and-projection portions including a depression portion and a projection portion flexed at an angle ranging from 10 to 80 degrees relative to a main flow direction of said exhaust gas to be continuous with each other.
 8. A heat exchanger according to claim 7, wherein said plurality of heat-exchange tubes are each formed so that an angle of said wavelike depression-and-projection portions in a region positioned in a vertically upper portion of the flat surface relative to the main flow direction of said exhaust gas is smaller than an angle of said wavelike depression-and-projection portions in a region positioned in a vertically lower portion of the flat surface relative to the main flow direction of said exhaust gas.
 9. A heat exchanger according to claim 8, wherein said plurality of heat-exchange tubes are each formed so that the angle of said wavelike depression-and-projection portions in the region positioned in the vertically upper portion of the flat surface relative to the main flow direction of said exhaust gas falls within a range of 10 to 45 degrees and the angle of said wavelike depression-and-projection portions in the region positioned in the vertically lower portion of the flat surface relative to the main flow direction of said exhaust gas falls within a range of 45 to 80 degrees. 